This invention relates generally to prosthetic heart valves, and more particularly to porcine xenograft heart valves, and their methods of preparation.
Traditionally, porcine heart valves are treated with a cross-linking agent or tanning fluid in order to stabilize the tissue against degradation. There have been a variety of approaches taken, but most involve exposure of the porcine valve to glutaraldehyde or other cross-linking agent, with the valve displaying a configuration in which the leaflets are closed. Maintaining the leaflets in closed position has typically been accomplished by providing a pressure differential across the valve. Pressure differential is used in a range from less than 4 mm Hg, as set forth in U.S. Pat. No. 4,372,743, issued to Lane, up to 120 mm Hg, as disclosed in U.S. Pat. No. 4,050,893, issued to Hancock et al. Fixation has also been accomplished without a pressure differential across the valve, in which case the valve is fixed with leaflets assuming a relaxed, neutral position. One such method is suggested in the article "Influence of Fixation Conditions on the Performance of Glutaraldehyde-Treated Porcine Aortic Valves: Towards a More Scientific Basis", by Broom et al, published in Thorax, Vol. 34, pp. 166-176, 1979.
An alternative method of fixing heart valve tissue is set forth in U.S. Pat. No. 3,966,401, issued to Hancock et al. In the method disclosed therein, the outflow side of the heart valve is coupled to a source of pressurized fixative, and the pressure applied to the outflow side of the heart valve is pulsed, from a high pressure level in the range of 80 to 120 mm, down to a low, or in some cases, negative pressure. It is believed that this process would provide a repetitive ballooning and relaxing of the aorta and valve leaflets. However, actual fluid flow through the valve is not disclosed, and it is believed that this process would not result in the repetitive opening and closing of valve leaflets during fixation.